1. Technical Field
The invention relates to light emitting diodes. In particular, the invention relates to light emitting diodes fabricated from nanostructures.
2. Description of Related Art
Semiconductor devices that generate or emit light are used in and often as a backbone of many modern optoelectronic or photonic systems. In particular, most modern optical communication systems depend on light emitting semiconductor devices for one or more of signal generation, signal regeneration/amplification, and signal modulation (i.e., direct modulation). Light emitting semiconductor devices are devices that generate light through carrier or exciton recombination in a vicinity of a semiconductor junction. Examples of light emitting semiconductor devices include, but are not limited to a light emitting diode (LED) and a semiconductor diode-based laser (i.e., solid-state laser).
In recent years, light emitting semiconductor devices of very small size comprising one or more nanowires have been developed. In particular, semiconductor nanowires that incorporate an integral semiconductor junction have been demonstrated and employed to realize nanowire-based LEDs and semiconductor lasers. Such light emitting semiconductor devices that employ a semiconductor nanowire, either singly or in a plurality, may be attractive for use in a wide variety of applications. In particular, nanowire light emitting semiconductor devices provide additional degrees of freedom in manipulating performance characteristics of such devices that may not be available in conventional devices based solely on bulk semiconductor properties.
Among key limiting performance characteristics of such light emitting semiconductor devices that employ exciton recombination are light emission efficiency and rate of light emission (e.g., switching speed). Light emission efficiency relates to how many of an available number of excitons or exciton pairs in the semiconductor junction actually produce useful emitted light. Related to light emission efficiency is optical output power which may include a measure of how much of the light that is produced is actually emitted in a useful direction. The rate of light emission or electro-optical response time is a measure of how fast the semiconductor device can respond to a change in a voltage bias, for example. The light emission rate is closely related to a recombination rate of the semiconductor junction which, in turn, is related to a probability that a hole/electron pair (i.e., an exciton) will recombine within the semiconductor junction. The light emission rate may limit a modulation rate of a light emitting semiconductor device, for example.
Efforts to overcome limitations associated with light emission efficiency and light emission rate have generally focused on modifying inherent properties of a semiconductor material or materials used to construct the light emitting semiconductor devices. Examples of such effort include attempts to remove or strictly control crystal defects within a crystal lattice of the semiconductor material and various methods related to increasing an optical field intensity within the semiconductor junction. Inclusion of a quantum well within the semiconductor junction (e.g., quantum dots in a nanowire semiconductor junction) has proved useful in increasing the light emission rate. However, there is still a keen interest in developing means for further enhancing one or both of the light emission efficiency and light emission rate of light emitting semiconductor devices. Providing such means would satisfy a long felt need.